U.S. Pat. No. 4,271,538, issued to Edward N. Montesi et al, discloses a pair of safety spectacles having a one-piece front or facepiece shaped to wrap around the wearer's eyes and having temples pivotally attached thereto. The one-piece front includes a central optical portion of the "mono lens" type having a single optical axis and a corrected optical curve for zero refractive power. The front and the temples each include inwardly projecting upper and lower flanges to enclose the region between the spectacles and the wearer's face and thereby increase the degree of protection. Owing to such enclosure, however, the rear surface of the front is relatively poorly ventilated and is thus susceptible to fogging.
The patent specification teaches that the temples may be provided with air vents of various types, and specifically discloses the use of louvers for providing desired ventilation. The disclosed louvers are angled so as to direct air inwardly and forwardly against the rear surface of the one-piece front. Owing to the practicalities of mold design, however, the louvers do not overlap, as viewed from the side, creating the possibility for injury to the eyes or face from projectiles or the like. Further, the louvers have a relatively small extent in the direction of the airflow, and hence cannot efficiently direct air against the rear surface of the lens front.